The use of various thermoplastic resins to make fibers and fabrics is well known. In particular, propylene-based polymers and copolymers (and in particular, propylene-based elastomers) are well known in the art for their usefulness in a variety of applications, including the manufacture of nonwoven fabrics. Such fabrics have a wide variety of uses, such as in medical and hygiene products, cleaning devices, clothing, filter media, and sorbent products. Nonwoven fabrics are particularly useful in hygiene products, such as baby diapers and wipes, adult incontinence products, training pads, puppy pads, and feminine hygiene products. An important aspect of these fabrics, particularly in hygiene applications, is the ability to produce aesthetically pleasing fabrics, i.e., fabrics that are soft to the touch, and that have good leakage performance, i.e., fabrics that are stretchable and conform to the body of the wearer.
Production of nonwoven fabrics using commercially available propylene-based polymers having a melt flow rate (MFR) less than 50 g/10 min in the elastic layers can be difficult, because the low MFR of such polymers requires high melt temperatures and high pressures to melt blow into fibers. High process temperatures can cause undesirable degradation in the extruder, while high pressures limit the throughput rate of the melt blowing equipment, as illustrated in FIG. 3. Previously, some propylene-based polymers have been blended with an additional polymer or polymers post-reactor, often isotactic propylene homopolymers, and then visbroken with peroxide to achieve a higher MFR polymer for use in elastic layers. These additional process steps typically increase manufacturing cost and complexity to the process and may reduce the elastic performance of the resulting nonwoven fabrics.
Moreover, production of nonwoven fabrics using commercially available propylene-based polymers having these desirable attributes of softness and leakage performance can be obtainable by including a selection of additives such as slips and/or by modifying of processing conditions to achieve a certain fiber size. Some slip agents may migrate out of the polymer during processing and can deposit on equipment.
International Patent Application No. PCT/US2014/036335, describes propylene-based compositions for meltspun nonwoven compositions. International Patent Application No. PCT/US2014/042119, describes blends of propylene-based elastomers and broad molecular weight polypropylene or impact copolymers for use in nonwoven articles. International Patent Application No. PCT/US2014/042127, describes blends of propylene-based elastomers and impact copolymers for use in nonwoven articles.
It is therefore desirable to form the elastic layers of nonwoven fabrics from propylene-based polymers having a higher MFR (i.e., greater than 50 g/10 min) without additional complex steps to the existing manufacturing process. Such fabrics can be produced under broader process conditions, and at higher throughput rates and lower costs. It would also be desirable to form fabrics that exhibit a desirable balance of retractive force and permanent set, and form nonwoven fabrics with high barrier properties. It is appreciated that such fabrics can be used for thermal and sonic insulation.